This description relates to incorporating electronic devices in a paper or other sheet.
A variety of items have been incorporated into paper for security and other purposes. These items include so-called security threads that can be seen by the human eye either directly or when the paper is held up to normal light or subjected to a special light source. Some items that are incorporated in the paper can be generally invisible to the human eye but detected and read by special techniques and devices. Some of these approaches are used in currency, for example, as a security measure.
The item to be embedded in the paper may be formed as a continuous strip of material that may or may not bear items on the strip of material. In some cases, the items that are on the strip and are to be embedded are discrete items, for example, integrated circuits (also referred to as ICs or as chips). The discrete items can be mounted or formed on a continuous strip of material that is embedded into the paper together with them. In this case, the strip of material is referred to as a carrier strip because it carries the discrete items.
In some cases, the items that are incorporated into the paper are embedded within the paper and not exposed at the surface of the paper. In some cases, portions of the items may be exposed at the surface.
Embedding such an item into paper can be done in a variety of ways, for example, by sandwiching the item between two layers. In some cases, such an item can be embedded during the process of making paper from a fiber slurry. The thickness of the item embedded in the paper during the process of making paper is such that the item would not give rise to any perceptible extra thickness in the vicinity of the paper containing the item. In other cases, the item is formed on the surface of the paper.
The material for the strip can be made of a material that is impermeable to the fiber slurry, such as paper, or an organic film, or metal foil, or a combination of them. The material for the strip can also be porous, or permeable to the fiber slurry, which enables the formation of paper around it when the paper is made from the fiber slurry. The strip materials can be dispersible in water, in a solvent, or removed by melting.
The item embedded in the paper can be an electronic device comprising a chip or chips. The electronic device can be fabricated using known semiconductor techniques such as thin-film methods on conventional silicon substrates or on layered silicon-insulator-silicon substrates, methods for inorganic printed electronics, or methods for organic electronics.
In some cases, the chip can be an RFID (radio frequency identification) chip. In general, RFID chips incorporated in paper can be associated with antennas that enable communication between the chips and the outside world. The chip may be placed in a non-conductive portion of the carrier strip and electrically connected (attached) to an antenna formed on the carrier strip. In some cases, the antenna formed on the carrier strip is a dipole antenna made of two conductive strips the size of which corresponds to the size of the paper. The chip may have an integrated, on-chip, antenna. The on-chip antenna may be inductively coupled to inductors placed on the carrier strip. In some cases, the on-chip antenna can be coupled to an additional antenna fabricated on a surface of the paper. In some cases, the chip is flush in a surface of the paper and attached to an antenna additionally formed on the surface.